Multicast meeting unit and multicast meeting program

ABSTRACT

The invention provides a television meeting unit that is capable of displaying a picture smoothly on a middle participation terminal. To realize such television meeting unit, the multicast meeting unit is provided with a picture coding means for coding an input picture, a picture transmission means for transmitting the coded picture by mean of multicast, a picture receiving means for receiving the transmitted coded picture, a picture decoding means for decoding the received picture, a picture display means for displaying the decoded picture, a middle participation notice means for notifying middle participation in a meeting, and a middle participation terminal detection means for detecting the middle participation notice and for transmitting it to the picture coding means. The picture coding means, upon receiving the middle participation notice from the middle participation terminal detection means, changes the coding format to the in-frame coding format.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a television meeting unit, atelevision meeting system, and a method for controlling a televisionmeeting system, and particularly relates to a television meeting unit, atelevision meeting system, and a method for controlling a televisionmeeting system capable of shortening the time required to display apicture of meeting participants to a new participant who participates inthe middle of a meeting.

[0003] 2. Description of Prior Art

[0004] Heretofore, a unit for multiplying the picture and voice atmultiple points, namely so-called MCU (Multipoint Control Unit), isneeded to hold a television meeting between multiple points.

[0005] However, with development of the Internet recently, the groupbroadcast function so-called multicast has been available, and as theresult it becomes possible by use of the multicast to hold an electronicmeeting between multiple points without preparation of a particular unitsuch as MCU.

[0006]FIG. 1 and FIG. 2 show a typical exemplary. structure of amulticast television meeting system that uses the picture and voice.FIG. 1 shows a connection diagram to a network, and FIG. 2 is afunctional block diagram for showing a schematic structure of terminalunit. The picture and voice generated from the respective terminal units12-1 to 12-x are transmitted broadcasterly to the respective terminalunits 12-1 to 12 x, and the received picture and voice are displayedindividually or in the synthesized form to realize the televisionmeeting.

[0007] The picture and voice of a television meeting system in the formof compressed code are transmitted usually because of the communicationcapacity restriction. Typically, H. 261 format or MPEG1 format is usedas the picture compression coding system. In these picture compressioncoding systems, the in-frame coded picture in which the pixel value iscoded as it is and the inter-frame prediction coded picture are usedwith switching selectively. The time redundancy of the picture withslight motion and change is reduced by use of the inter-frame predictioncoded picture in which the difference between the previous frame and thenext frame is coded because the next frame is very similar to theprevious frame. On the other hand, in the case of the picture with quickmotion or scene change, the in-frame coded picture is used effectivelyin which the pixel value is coded as it is used effectively because thecorrelation between frames is slight. In the general television meeting,the in-frame coded picture is transmitted at first and then theinter-frame coded picture is transmitted thereafter because the motionis not so quick.

[0008] At first in the case that a participant terminal participates inthe middle in the conventional multicast meeting unit, the newparticipant receives the inter-frame prediction coded picture that isthe meeting data served up to that time. Therefore, the terminal thatparticipates in the middle and receives the inter-frame prediction codedpicture cannot display a normal picture because no reference picture(in-frame coded picture) is available, or cannot display the pictureuntil it receives an in-frame coded picture.

[0009] At second in the case that the processing capability of the newparticipant terminal is different, it is required for every participantterminal to perform with a set value within the processable range andfurthermore it is required to change the set value due to the middleparticipation.

SUMMARY OF THE INVENTION

[0010] To solve the above-mentioned problem, the present invention isprovided with a function that a middle participation information istransmitted when a terminal (middle participation terminal) participatesin a meeting in the middle, and other terminals (already participatingterminal) receive and detect the information and transmit the in-framecoded picture (I-frame) instead of the inter-frame prediction codedpicture when the already participating terminals transmit the data.Thereby, it becomes possible to display a picture smoothly (a picture ofa meeting can be displayed in a short time) to the terminal thatparticipates in the middle and the multiple point television meeting isheld smoothly by use of a multicast meeting unit.

[0011] Furthermore, the present invention is provided with a functionthat the processing capability information on terminals that areparticipating in a meeting and terminals that are to participate in themeeting is held, collated, and converted to the coded parameter that isprocessable by any terminal. Thereby, the information is converted so asto be processable by any terminal in the case that it is required toconvert the coding parameter due to the middle participation.

[0012] Furthermore, the present invention is provided with a functionthat the priority adding function to terminals that precipitate in ameeting and terminals that are to participate in the meeting, and thecoding parameter of the important data is converted. Thereby, theindividual terminals are coded correspondingly to the priority, and theimportant subject is discussed preferentially in the meeting.

[0013] Furthermore, the present invention is provided with a functionthat the priority of the terminals are managed so as to avoid the bandover due to I-frame broadcast transmission by adjusting the middleparticipation and the terminal performance difference to transmitI-frame from the terminal of the higher priority. Thereby, a picture ofthe terminal of the higher priority is displayed first, and the pictureof other meeting participants is displayed later, and as the result apicture of the terminal of higher priority can be displayed earlierwithout adverse effect on the band of the network.

[0014] Therefore, the first object of the present invention is toshorten the time for waiting the display of a picture received by themiddle participation terminal in a multicast meeting unit.

[0015] The second object of the present invention is to make the codingparameter acceptable to every terminal even in the case that the codingparameter, which has been used by every terminal, becomes unacceptableto a part of terminals due to the middle participation in the meeting.

[0016] The above-mentioned objects and advantages of the presentinvention will be apparent based on the embodiments described in detailhereinafter with reference to the drawings.

BRIEF DESCRIPTION OF THE INVENTION

[0017]FIG. 1 is a functional block diagram showing the connection of aconventional multicast multiple point meeting system to a network.

[0018]FIG. 2 is a functional block diagram showing the schematicstructure of the terminal unit of the conventional multicast multiplepoint meeting system.

[0019]FIG. 3 is a functional block diagram showing the schematicstructure of a multicast meeting unit in accordance with the firstembodiment of the present invention.

[0020]FIG. 4 is a diagram showing the data structure of a transmitterinformation in the first embodiment.

[0021]FIG. 5 is a functional block diagram showing the schematicstructure of a multicast meeting unit to which a reception noticedetection means is added in the first embodiment.

[0022]FIG. 6 is a functional block diagram showing the schematicstructure of a multicast meeting unit to which a network error ratemeasurement means is added in the first embodiment.

[0023]FIG. 7 is a diagram showing a method of middle participationnotice by use of multicast in the first embodiment.

[0024]FIG. 8 is a diagram showing a method of middle participationnotice by use of unicast in the first embodiment.

[0025]FIG. 9A and FIG. 9B are diagrams showing the picture coding formattransmitted in the present invention, in which

[0026]FIG. 9A represents the picture coding format in the case that amulticast meeting is continuing without the middle participation, and

[0027]FIG. 9B represents the picture coding format that is convertedfrom P-picture coding to I-picture coding in the case that a middleparticipation notice is detected during the meeting.

[0028]FIG. 10 is a functional block diagram showing the schematicstructure of a multicast meeting unit in accordance with the secondembodiment of the present invention.

[0029]FIG. 11 is a diagram showing the data structure of the priorityinformation in the second embodiment.

[0030]FIG. 12 is a diagram showing the table structure that holds thepicture coding information, the state that appears when a terminalparticipates in a meeting in the middle and when a terminal withdrawsfrom the meeting, and one example of the picture coding format used inthe meeting at that time.

[0031]FIG. 13 is a functional block diagram showing the schematicstructure of a multicast meeting unit in accordance with the thirdembodiment of the present invention.

[0032]FIG. 14 is a functional block diagram showing the schematicstructure of a multicast meeting unit (cellular telephone) in accordancewith the fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Embodiments of the present invention will be described in detailwith reference to FIG. 3 to FIG. 14. The present invention is by nomeans limited to these embodiments, and can be applied with variousmodifications without departing from the spirit and the scope of thepresent invention.

[0034] (First Embodiment)

[0035] At first, the configuration for displaying a picture smoothly ona terminal that participates in a meeting in the middle will bedescribed hereinafter. FIG. 3 is a functional block diagram showing theschematic structure of the first embodiment of a multicast televisionterminal unit (simply referred to as “terminal unit” hereinafterdepending on the case) of the present invention. In FIG. 3, 100 denotesa terminal unit, and the terminal unit is connected to a network andused like the system shown in FIG. 1. The terminal unit 100 supplies apicture data obtained from a picture input means 101 to a picture codingmeans 102, the picture coding means 102 compresses and codes thesupplied picture data and supplies it to a picture transmission means103, and the picture transmission means 103 transmits the compressed andcoded picture data to the network. At that time, the picture codingmeans 102 changes the coding method when it obtains a middleparticipation information from a middle participation detection means113.

[0036] Similarly, the terminal unit 100 supplies the voice data obtainedfrom a voice input means 104 to a voice coding means 105, the voicecoding means 105 compresses and codes the supplied voice data andsupplies it to a voice transmission means 106, and the voicetransmission means 106 transmits the compressed and coded voice data tothe network. A picture receiving means 107 receives the compressed andcoded picture data from the other terminal unit and supplies it to apicture decoding means 108. A plural number of picture decoding means108 corresponding to the number of other terminal units are provided,each picture decoding means 108 codes the compressed and coded picturedata so as to match with a corresponding terminal and supplies it to apicture display means 109. The number of picture display means 109corresponds to the number of other terminal units. Each picture displaymeans 109 displays a picture of a corresponding terminal.

[0037] Similarly, a voice receiving means 110 receives the compressedand coded voice data from the other terminal unit, and supplies it to avoice decoding means 111. The number of voice decoding means 111corresponds to the number of other terminal units. Each voice decodingmeans 111 decodes the compressed and coded voice data for acorresponding terminal, and supplies it to a voice output means 112. Thenumber of voice output means 112 corresponds to the number of otherterminal units. Each voice output means 112 outputs the voice of acorresponding terminal. A middle participation notice means 114 suppliesa middle participation notice to the network when a terminal unitparticipates in the middle. FIG. 4 shows an example of a picture datapacket to which a transmitter information has been added that istransmitted by the middle participation notice means 114. An example ofthe middle participation notice data, which is transmitted when a middleparticipation is notified, includes the data in which an addressinformation on a transmittee and a transmitter information on a middleparticipation terminal are placed adjacently.

[0038]FIG. 5 is a functional block diagram showing the schematicstructure to which a reception notice detection means is added. In FIG.5, 116 denotes a reception notice transmission means for transmitting areception notice when a middle participation terminal receives anin-frame coded picture from the other meeting terminal, and 115 denotesa reception notice receiving means of a (the other) meeting terminal forreceiving a reception notice that has been transmitted from a middleparticipation terminal through the reception notice transmission means116 (described in detail hereinafter).

[0039]FIG. 6 is a functional block diagram showing the schematicstructure to which a network error rate measurement means has beenadded. In FIG. 6, 117 denotes a network error rate measurement means formeasuring the network error rate when the picture data is obtained fromthe picture receiving means 107 (described in detail hereinafter).

[0040]FIG. 7 shows a method of middle participation notice that uses themulticast, and FIG. 8A and FIG. 8B show methods of middle participationnotice that use the unicast. Furthermore, FIG. 9A and FIG. 9B showcoding formats that code a picture signal transmitted from the picturecoding means 102. Out of these figures, FIG. 9A is a diagram for showinga coding format of a transmitted picture signal that is usedconventionally and is used when a multicast meeting is continued withouta middle participation in the present invention. Furthermore, FIG. 9B isa diagram for showing a method for changing the P-picture coding formatto the I-picture coding format when a middle participation notice isreceived during the middle of a meeting, which is employed in thepresent invention. In FIG. 9A and FIG. 9B, I denotes the I-picture(in-frame coded picture), and P denotes the P-picture (inter-frameforward prediction coded picture).

[0041] The operation will be described herein under on the terminal unithaving the above-mentioned structure. The picture data supplied from thepicture input means 101 such as a camera is supplied to the picturecoding means 102. The picture coding means 102 changes the coding formatas described hereinafter based on the information supplied from themiddle participation means 113, and compresses and codes the picturedata. The compressed and coded picture data is transmitted to thenetwork from the picture transmission means 103 by use of the multicast.

[0042] The voice data supplied from the voice output means 104 such as amicrophone is supplied to the voice coding means 105. The voice codingmeans 105 compresses and codes the voice data. The compressed and codedvoice data is transmitted to the network from the voice transmissionmeans 106 by use of the multicast. The picture data transmitted from theother terminal unit is received by the picture receiving means 107through the network. The picture receiving means 107 supplies thereceived picture data to the picture decoding means 108-1˜ncorresponding to the respective other terminal units with reference tothe transmitter information on the picture data. One example of thetransmitter information that is embedded in the data to be transmittedis shown in FIG. 4. The number of picture decoding means 108-1˜ncorresponds to the number of other terminal units. Each picture decodingmeans decodes the picture data to be transmitted to the picture displaymeans 109-1˜n. The number of picture display means 109-1˜n correspondsto the number of other terminal units. Each picture display meansdisplays the decoded picture data on a display.

[0043] The voice data transmitted from the other terminal unit isreceived by the voice receiving means 110 through the network. The voicereceiving means 110 supplies the received voice data to the voicedecoding means 111-1˜n corresponding to the respective other terminalunits with reference to the transmitter information on the voice data inthe same manner as used in the case of the picture data. The number ofvoice decoding means 111-1˜n corresponds to the number of other terminalunits. Each voice decoding means decodes the voice data and supplies itto the voice output means 112-1˜n. The number of voice output means112-1˜n corresponds to the number of other terminal units. Each voiceoutput means outputs the decoded voice data from a speaker. Otherwise, amethod, in which one terminal is provided with not a plurality of voiceoutput means, but one terminal is provided with one voice output meansby providing a voice synthesis means so-called mixer between the voicedecoding means and the voice output means, may be employed.

[0044] When the terminal unit participates in a meeting in the middle,the middle participation notice means 114 notifies the other terminalsof the middle participation through the multicast or unicast.

[0045] In the case that the middle participation is notified through themulticast, the middle participation notice means 114 notifies the otherterminals of the middle participation simultaneously as shown in FIG. 7.On the other hand, in the case that the middle participation is notifiedthrough the unicast, two methods may be available as shown in FIG. 8. Inthe one method, the address of meeting terminals that are participatingin a current meeting has been obtained previously and the middleparticipation is supplied individually as shown in FIG. 8A. In the othermethod, the middle participation is supplied to any one meeting terminalamong meeting terminals that are currently participating in a meetingand the meeting terminal that has received the middle participationpropagates it to the other meeting terminal successively as shown inFIG. 8B.

[0046] <Method for Changing Coding>

[0047] Methods shown in FIG. 9A and FIG. 9B are exemplified as themethod for changing the coding format in the picture coding means 102.

[0048] In the case of the conventional transferred picture coding formatas shown in FIG. 9A, a middle participation terminal receives aP-picture because terminals that are participating in a meetingcurrently transmit the P-picture when the middle participation terminalparticipates in the meeting in the middle. The middle participationterminal that receives the P-picture cannot decode a normal picturebecause the middle participation terminal has no I-picture, which is thereference picture.

[0049] However, it is possible to change the coding method when a middleparticipation terminal participates in a meeting in the middle becausecurrent participation terminals receive a middle participation notice.Therefore, the current terminals that are participating in the meetingreceives the middle participation notice at the middle participationdetection means 113 when the middle participation terminal participatesin the meeting in the middle, and the information is supplied to thepicture coding means 102. In response to the information, the picturecoding means 102 that has continued coding to P-picture until nowchanges the coding format to I-picture that can be decoded singularly.

[0050] <Method for Setting I-Picture Sending Term>

[0051] Three I-picture sending terms are available as described hereinunder.

[0052] In the first method, the I-picture is sent for a certain time.One frame picture data of changed coding method or a certain number offrames of changed coding method is sent out, and the coding method ischanged to the original coding method thereafter. In the second method,when the middle participation terminal receives an in-frame codedpicture from other meeting terminals, the middle participation terminalissues a reception notice to other meeting terminals, and other meetingterminals change the coding method to the original coding method. Thesecond method will be described with reference to FIG. 5.

[0053] When the picture receiving means 107 of the middle participationterminal receives an I-picture from other meeting terminals, theinformation for notifying the reception is supplied to the receptionnotice transmission means 116. The reception notice transmission means116 transmits a reception notice to other meeting terminals by use ofthe multicast as shown in FIG. 7 or by use of the unicast as shown inFIG. 8A. When the unicast is used, the transmitter information shown inFIG. 4 included in the received I-picture is used to specify thetransmitter.

[0054] Other meeting terminals receive the reception notice through thereception notice receiving means 115, the information for notifyingreception of the reception notice is supplied to the picture codingmeans 102, and the picture coding means 102 changes the picture codingformat to the original format.

[0055] Because other meeting terminals can recognize that the middleparticipation terminal has received the reference picture (I-picture),other meeting terminals can continue to transmit the reference pictureuntil the middle participation terminal receives the reference picture.

[0056] In the third method, the network error rate is measured, othermeeting terminals continue to use the changed coding format and transmitthe reference picture for only the time corresponding to the error rate.The third method will be described with reference to FIG. 6.

[0057] The network error rate measurement means 117 measures the errorrate in the picture data received through the picture receiving means107 based on, for example, the sequence number embedded in the picturedata, and the measured error rate is supplied to the picture codingmeans 102. The picture coding means 102 determines the reference framesending term shown in FIG. 9 depending on the error rate supplied fromthe network error rate measurement means 117. In detail, the doubledreference frame sending term may be employed for the doubled error rate.For example, if the reference picture of two frames is transmitted atthe time of the middle participation under the condition that one packeterror is included in 100 packets, the reference picture of doubled,namely four, frames is transmitted at the time of the middleparticipation when the error rate is doubled (the condition that twopacket errors are included in 100 packets).

[0058] Because the picture receiving means 107 receives the picture datafrom a plurality of meeting terminals, the mounting method that satisfythe highest error rate may be employed. It is apparent that this methodmay be used for the middle participation terminal and other meetingterminals. Thereby, a plurality of I-picture, namely reference picture,can be sent out in the case that the network error rate is high, theprobability of reception of the reference picture by the middleparticipation terminal is improved with minimized load on the network.By using the structure described hereinbefore, it is possible to displaythe picture of a meeting within a short time by use of the multicasttelevision meeting unit even though a terminal participates in themeeting in the middle, and the multiple point television meeting can becontinued smoothly.

[0059] (Embodiment 2)

[0060] Next, a mechanism for exchanging the processing capabilityinformation on each terminal so that all the terminals participating ina meeting can display the picture and a mechanism for giving thepriority to the data that is important in the meeting will be described.FIG. 10 is a functional block diagram showing the schematic structure ofthe second embodiment of a multicast television meeting terminal unit ofthe present invention. In FIG. 10, 800 denotes a terminal unit, and theterminal unit is connected to a network and used.

[0061] The terminal unit 800 supplies the picture data obtained from apicture input means 801 to a picture coding means 802, the picturecoding means 802 compresses and codes the supplied picture data andsupplies it to a picture transmission means 803, and the picturetransmission means 803 transmits the compressed and coded picture datato the network. At that time, the picture coding means 802 obtains amiddle participation information from a picture receiving means 807 andchanges the coding method. The terminal name of the middle participationterminal and the picture data (coding format, parameter) transmittedfrom the middle participation terminal are held in a coding stateholding means 813.

[0062] Similarly, the voice data obtained from a voice input means 804is supplied to a voice coding means 805, the voice coding means 805compresses and codes the supplied voice data and supplies to a voicetransmission means 806, and the voice transmission means 806 transmitsthe compressed and coded voice data to the network. At that time, theinformation such as voice level is supplied from the voice input means804 to an significance information adding means 814. Furthermore, thevoice coding means 805 obtains the voice coding format or voice codingparameter from a voice receiving means 810 and changes the codingmethod. Furthermore, the picture receiving means 807 receives thecompressed and coded picture data from the other terminal unit throughthe network, and supplies it to a picture decoding means 808. At thattime, the received picture information is supplied to the picture codingmeans 802. The number of picture decoding means 808 corresponds to thenumber of other terminal units, and the compressed and coded picturedata is decoded so as to match with each terminal and supplied topicture display means 809. The number of picture display means 809corresponds to the number of other terminal units. The picture displaymeans displays a picture of each terminal.

[0063] Similarly, the voice receiving means 810 receives the compressedand coded voice data from the other terminal unit through the network,and supplies it to a voice decoding means 811. The number of voicedecoding means 811 corresponds to the number of other terminal units,and the compressed and coded voice data is decoded so as to match witheach terminal and supplied to a voice output means 812. The number ofvoice output means 812 corresponds to the number of other terminalunits. The voice output means outputs the voice of on each terminal.

[0064] <Significance Information Addition>

[0065]FIG. 11 shows one example of a picture data packet that is to betransmitted to which the significance information is added. FIG. 12shows an example of the structure of a table for holding the picturecoding information, the state of middle participation and middlewithdrawing, and the picture coding format used in the meeting at thattime.

[0066] The operation of the terminal unit having the structure describedhereinabove will be described herein under.

[0067] The picture data taken in from the picture input means 801 suchas camera is supplied to the picture coding means 802, and the picturedata is compressed and coded.

[0068] A method described hereinunder, in which the middle participationis detected by the picture receiving means 807 without using the middleparticipation notice means 114 as in the case of the embodiment 1 whenthe picture coding means 802 compresses and codes the picture data, maybe employed.

[0069] The picture receiving means 807 refers the transmitterinformation on the received picture data as shown in FIG. 4. If thetransmitter information is a transmitter information on a terminal otherthan current participation terminals, the transmitter information isjudged as that of a middle participation terminal, and the informationfor notifying participation of the middle participation terminal issupplied to the picture coding means 802.

[0070] As an exemplary “method for discrimination between the currentparticipation terminal and the middle participation terminal”, a methodin which the transmitter information on the current participationterminals is stored in a memory of each terminal may be employed. In thecase that the data having the transmitter information that is not storedin the memory is supplied, it is possible to judge the data to indicateparticipation of a middle participation terminal.

[0071] The middle participation is detected as described hereinabove,and the picture coding means 802 changes the coding format to thein-frame coded picture (reference picture) as shown in FIG. 9. As theresult, it is possible to display the picture of other meeting terminalson the middle participation terminal within a short time.

[0072] The compressed and coded picture data is transmitted to thenetwork through the picture transmission means 803. The picturetransmission means 803 can add the significance to the picture data asshown in FIG. 11 when the picture data is transmitted. The significancerepresents the dynamic significance in the meeting such as a speaker. Amethod may be employed, in which when the level of significance of aspeaker is up, the voice input level supplied from the voice input means804 is supplied to the significance information adding means 814, andthe significance information adding means 814 adds the significancecorresponding to the voice level. The picture quality is improved, theframe rate is increased, or the picture size may be changed by use ofthe picture coding means 802 for the case of the picture data of highsignificance.

[0073] For example, the processing is performed normally at aperformance value (parameter): B that is lower than the performancevalue (parameter): A of the terminal having the lowest performance basedon the processing capability information exchange (<that will bedescribed hereinafter as <parameter setting relevant to the processingcapability of the terminal>) with emphasis on the saving of NW band andimmediate data processing, and only when the data to which thesignificance is added comes, the level of the performance value is up toa higher value within a range lower than the performance value A for thedata with significance. As described hereinabove, the quality of thepicture supplied from a terminal that is considered to be important suchas a speaker in the meeting is changed dynamically, and as the resultthe quality of a picture that attracts attentions of participants isimproved. The voice data supplied from the voice input means 804 such asa microphone is supplied to the voice coding means 805. The voice codingmeans 805 compresses and codes the voice data. The compressed and codedvoice data is transmitted to the network by use of the multicast throughthe voice transmission means 806.

[0074] The picture data transmitted from other terminal units isreceived by the picture receiving means 807 through the network. Thepicture receiving means 807 supplies the received picture data to thepicture decoding means 808-1˜n corresponding to the respective otherterminal unit with reference to the transmitter information on thepicture data. The number of picture decoding means 808-1˜n correspondsto the number of other terminal units. Each of the picture decodingmeans 808-1˜n decodes the picture data and supplies it to the picturedisplay means 809-1˜n. The number of picture display means correspondsto the number of other terminal units similarly, and the decoded picturedata is displayed on a display.

[0075] The voice data transmitted from the other terminal units isreceived by the voice receiving means 810 through the network. The voicereceiving means 810 supplies the received voice data to the voicedecoding means 811-1˜n corresponding to the respective terminal unitswith reference to the transmitter information on the voice data. Thenumber of voice decoding means 811-1˜n corresponds to the number ofother terminal units. Each of the voice decoding means 811-1˜n decodesthe voice data and supplies it to the voice output means 812-1˜n. Thenumber of voice output means 812-1˜n corresponds to the number of otherterminal units similarly, and the decoded voice data is outputted from aspeaker. In some cases a method may be employed, in which one terminalis provided with not a plurality of voice output means, but one terminalis provided with only one voice output means with aid of a voicesynthesis means so-called mixer interposed between the voice decodingmeans and the voice output means.

[0076] Examples of the significance addition includes a case in whichsignificance is added depending on the user, that is, the significanceis up for the user of the chairman, and a case in which a highsignificance is added to a terminal displaying the significant picturemotion, other than the case in which the high significance is addeddepending on the input level of the voice. Furthermore, a method inwhich the picture coding means 802 changes the picture coding formatwill be described herein under. A method shown in FIG. 9 is exemplifiedas a method in which the picture coding means 802 changes the codingformat similarly to the embodiment 1.

[0077] <Parameter Setting Relevant to Processing Capability ofParticipation Terminal>

[0078] The processing capability information exchange will be describedas the premise for adding the above-mentioned significance. A middleparticipation terminal codes the data by use of the coding format andparameter that are relevant to the processing capability (CPUperformance) and supplies it to other meeting terminals. The othermeeting terminals that have received it obtain the picture size, thenumber of frames, and the data quantity of the received pictureinformation, and then changes the coding format so as to fit thereceived data, and as the result the other meeting terminals can supplythe data that is relevant to the processing capability of the middleparticipation terminal.

[0079] A method for changing the coding will be described in detail withreference to FIG. 12A, FIG. 12B, and FIG. 12C. At first, in the initialstate of a meeting shown in FIG. 12A, terminals A, B, and C areparticipant in the meeting. In this state, because the picture codingparameter sent from the terminal A is lowest, the picture coding formatCIF, 10 fps, and 64 bps, that is the picture coding format of theterminal A, is used as the picture coding format in the meeting. Herein,the picture size CIF represents 352 (pixels)×288 (pixels), and QCIFrepresents 176 (pixels)×144 (pixels).

[0080] Next, the state in which the terminal D (QCIF, 5 fps, 32 kbps)participates in the meeting in the middle is shown in FIG. 12B. Herein,because the processing capability of the terminal D is lowest, thepicture coding format of the terminal D that is lowest in the processingcapability is used in the meeting in the same manner as used previously.Next, the state in which the terminal A and the terminal D withdraw fromthe meeting in the middle is shown in FIG. 12C. The data of the terminalA and the terminal D that have withdrawn from the meeting is deletedfrom the table, the picture coding information on the terminal C havingthe lowest processing capability among the residual terminals is usedsimilarly, and the meeting is continued by the residual meetingterminals. The level of the processing capability is defined in terminalunits herein. The reason is that all the values of the respective codinginformation are lower than those of other terminals. In the case thatthe terminal T1 has the picture size of the lowest value t1, theterminal T2 has the frame rate of the lowest value t2, and the terminalT3 has the bit rate of the lowest value t3, (t1, t2, and t3) are used asthe parameter for decision.

[0081] H. 323 capacity exchange has been known as a conventional methodfor determining parameters used by each terminal as describedhereinabove. In this method, after each terminal extends the session,parameters that can be encoded and decoded are exchanged each other anda meeting is continued by use of parameters that are usable each other.This method is possible only for 1:1 meeting, and IMCU should be usedfor using this method in the case that three or more terminalsparticipate. In this case, at first, each terminal transmits parametersthat can be encoded and decoded to MCU. Next, MCU detects parametersthat can be acceptable for all the terminals based on the parameterssupplied from each terminal, and transmits the parameter to eachterminal. Each terminal participates in the meeting by use of theparameters that have been detected by MCU.

[0082] However, because the structure of the present embodiment does notuse MCU, this method is not applied. In the present embodiment, themulticast address is acquired from DHCP server, and the picture andvoice are transmitted immediately. The parameter is changed to theparameter that is usable each other on the terminal side that hasreceived the picture and voice. Because each terminal decides theparameter based on the supplied picture and voice as describedhereinabove, the structure having no MCU can be employed. Furthermore,in the conventional method, all the terminals should transmit parametersto MCU, MCU re-detects the parameter that is usable for all theterminals and distributes the parameter to each terminal in the case aterminal participates in the meeting in the middle. However, in the caseof the present embodiment, these procedures can be eliminated, a middleparticipation terminal can transmit the picture and voice immediately,and the time required for the middle participation terminal toparticipate in the meeting is shortened.

[0083] The same is applied to the voice data, the middle participationterminal codes the voice data by use of the coding format and parameterthat are relevant to the processing capability and supplies it to othermeeting terminals, the other meeting terminals that receive it obtainthe coding format and coding parameter of the received voice informationand change the coding to the relevant coding to thereby supply the datathat is relevant to the processing capability of the middleparticipation terminal. As described hereinabove, in the presentembodiment, by changing the coding method to a method that is relevantto the received coding format (change the coding parameter), it ispossible to continue a meeting (the meeting data is displayed even on aterminal having the low processing capability) when a meeting terminalhaving a low processing capability participates in the meeting in themiddle. Furthermore, by using the significant information, the highsignificant picture such as the picture of a speaker is displayed withhigher picture quality.

[0084] The middle participation detection means 113 described in the,embodiment 1 and the coding state holding means 813 described in thesecond embodiment 2 may be used in combination to receive the middleparticipation notice through the middle participation detection means113. In this case, an exemplary method, in which the current codinginformation is held in the coding state holding means 813 and the codingformat is changed, may be realized.

[0085] (Embodiment 3)

[0086] Next, a mechanism for avoiding the inconvenience that the band isoccupied fully when all the terminals that are participating in ameeting transmit I-frame simultaneously in response to reception of anotice of middle participation will be described herein under.

[0087]FIG. 13 is a functional block diagram showing the schematicstructure of the third embodiment of a multicast television meetingterminal unit of the present invention.

[0088] In FIG. 13, 1100 denotes a terminal unit, and the terminal unitis connected to the network and used as in the case of the system shownin FIG. 1. The terminal unit 1100 supplies the picture data obtainedfrom a picture input means 1101 to a picture coding means 1102, thepicture coding means 1102 compresses and codes the supplied picture dataand supplies it to a picture transmission means 1103, and the picturetransmission means 1103 transmits the compressed and coded picture datato the network. At that time, the picture coding means 1102 changes thecoding method depending on the priority supplied from the prioritydecision means 1114. The coding information that is used before thechange is held in the coding state holding means 1113 in the same tableform as used in the embodiment 2.

[0089] The voice data obtained from a voice input means 1104 is suppliedto a voice coding means 1105, the voice coding means 1105 compresses andcoded the supplied voice data and supplies it to a voice transmissionmeans 1106, and the voice transmission means 116 transmits thecompressed and coded voice data to the network. Furthermore, a picturereceiving means 1107 receives the compressed and coded picture data fromthe other terminal unit through the network, and transmits it to apicture decoding means 1108. At that time, the received pictureinformation is supplied also to the priority decision means 1114. Thenumber of picture decoding means 1108 corresponds to the number of otherterminal units, and the compressed and coded picture data is decoded soas to match with each terminal and supplied to the display means 1109.The number of picture display means 1109 corresponds to the number ofother terminal units similarly, and the picture of each terminal isdisplayed.

[0090] Similarly, a voice receiving means 1110 receives the compressedand coded voice data from the other terminal unit through the network,and supplies it to the voice decoding means 1111. The number of voicedecoding means 1111 corresponds to the number of other terminal units,and the compressed and coded voice data is decoded so as to match witheach terminal and is supplied to the voice out means 1112. The number ofvoice output means 1112 corresponds to the number of other terminalunits, and the voice of each terminal is outputted.

[0091] The operation of the terminal unit having the structure asdescribed hereinabove will be described hereinafter. The picture datasupplied from the picture input means such as a camera is supplied tothe picture coding means 1102. The picture coding means 1102 changes thecoding format based on the priority information supplied from thepriority decision means 1114, and compresses and codes the picture data.

[0092] The priority information is prepared by the priority decisionmeans 1114 that has obtained the picture data information from thepicture receiving means 1107. For example, a promoter of the meetingassigns the priority to each terminal previously at the time before themeeting is held. In many cases, the terminal of the chairman is assigneda high priority, and a terminal used by a general participant isassigned a low priority. The picture coding means 1102 changes thepicture coding format according to the priority when a middleparticipation terminal is detected. For example, when a middleparticipation terminal is detected, other terminals change the codingformat from the in-frame prediction coded picture to the inter-framecoded picture as shown in FIG. 9. At that time, if all the terminalchanges the coding format simultaneously, the picture data quantitytransmitted through the network increases sharply to result in pressedband. To avoid the above-mentioned problem, the picture is changed tothe in-frame coding picture in the order successively from the terminalhaving the highest priority for transmission with reference to thepriority information. Thereby, the middle participation terminal candisplay the picture in the order according to the priority.

[0093] The compressed and coded picture data is transmitted from thepicture transmission means 1103 to the network by use of the multicast.The voice data supplied from the voice output means 1104 such as amicrophone is supplied to the voice coding means 1105. The voice codingmeans 1105 compresses and codes the voice data. The compressed and codedvoice data is transmitted from the voice transmission means 1106 to thenetwork by use of the multicast.

[0094] The picture data transmitted from the other terminal unit isreceived by the picture receiving means 1107 through the network. Thepicture receiving means 1107 supplies the received picture data to thepicture decoding means 1108-1˜n corresponding to the respective otherterminal units with reference to the transmitter information on thepicture data. The number of picture decoding means 1108-1˜n correspondsto the number of other terminal units. Each of the picture decodingmeans 1108-1˜n decodes the picture data and transmits the picture to thepicture display means 1109-1˜n. The number of picture display means1109-1˜n corresponds to the number of other terminal units similarly,and the decoded picture data is displayed on a display.

[0095] The voice data transmitted from the other terminal unit isreceived by the voice receiving means 1110 through the network. Thevoice receiving means 1110 supplies the received voice data to the voicedecoding means 1111-1˜n corresponding to the respective other terminalunits with reference to the transmitter information on the voice data.The number of voice decoding means 1111-1˜n corresponds to the number ofother terminal units, and the voice decoding means 1111-1˜n decode thevoice data and supply it to the voice output means 1112-1˜n. The numberof voice output means 1112-1˜n corresponds to the number of otherterminal units similarly, and the decoded voice data is outputted from aspeaker. In some cases a method may be employed, in which one terminalis provided with not a plurality of voice output means, but one terminalis provided with only one voice output means with aid of a voicesynthesis means so-called mixer interposed between the voice decodingmeans and the voice output means.

[0096] For example, a method shown in FIG. 9 that is similar to themethod described in example 1 may be exemplified as a method that isused by the picture coding means 1102 to change the coding format. Inthe present example, the (a part of) priority information is transmittedfrom the picture receiving means 1107 to the priority decision means1114, but the transmission is not necessarily required. For example, (1)the data transmission from 1107 to 1114 can be eliminated by holding thepriority information previously in the priority decision means 114 (adashed line in FIG. 13 indicates the case). Furthermore, for example,(2) only the information that indicates whether the I-frame is receivedor not (whether a middle participation terminal participates or doesnot) is supplied from the picture receiving means 1107 to the picturecoding means 1102, and the coding method is changed immediately or laterdepending on the information supplied from the priority decision means1114. As described hereinabove, various modifications may be employed.

[0097] As described hereinabove, in the present embodiment, by use ofthe structure described hereinabove, not only it is possible to displaythe picture data of a meeting within a short time as described in theexample 1 but also it is possible that the picture data of the terminalhaving the higher priority can be displayed earlier without pressing ofthe band of the network by use of the priority information. In thelatter case, for example, the picture data with high priority of, forexample, the chairman is displayed earlier and the picture data of othermeeting participants are displayed later generally.

[0098] (Embodiment 4)

[0099] In the present embodiment, the unit other than personal computerssuch as desktop or potable computers can be used as the terminal unitthat can participates in a meeting (including middle participation).FIG. 14 is a functional block diagram showing the schematic structure ofthe fourth embodiment of a terminal unit of the present invention. Thecellular phone is used as the terminal unit in the present embodiment.In FIG. 14, 400 denotes a cellular phone served as the terminal unit,and the cellular phone 400 is connected to the network and used as inthe case of the terminal unit 100 shown in FIG. 1. The cellular phone400 is provided with a picture input means 101 for receiving a picturesignal, a picture coding means 102 for receiving the picture signal fromthe picture input means 101 and for compressing and coding the picturesignal, a picture transmission means 103 for generating the compressedand coded transmission picture data, and a communication means 250 fortransmitting the compressed and coded picture data generated from thepicture transmission means 103 to the network as in the case of theterminal unit 100 described in the first embodiment.

[0100] Furthermore, the cellular phone 400 is provided with a voiceinput means 104 for receiving a voice signal, a voice coding means 105for receiving the voice signal from the voice input means 104 and forcompressing and coding the voice signal, and a voice transmission means106 for transmitting the compressed and coded voice data to thecommunication means 250.

[0101] Furthermore, the cellular phone 400 is provided with a picturereceiving means 107 for receiving the compressed and coded picture datasupplied from the other cellular phone or terminal unit through thenetwork, picture decoding means 108 for decoding the received picturedata, and picture display means 109 for displaying the decoded picture.The number of picture decoding means 108 corresponds to the number ofother cellular phones, and the supplied picture data is decoded so as tomatch with each cellular phone or terminal unit and is supplied to thepicture display means 109. The number of picture display means 109corresponds to the number of other cellular phones similarly, and thepicture display means display the picture on the respective terminals.

[0102] Furthermore, the cellular phone 400 is provided with a voicereceiving means 110, voice decoding means 111, and voice output means112 for receiving and reproducing the voice transmitted from the othercellular phone or terminal unit. The voice receiving means 110 receivesthe compressed and coded voice data from the other cellular phone orterminal unit through the network and supplies it to the voice decodingmeans 111. The number of voice decoding means 111 corresponds to thenumber of other cellular phones, and the compressed and coded voice datais decoded so as to match with each terminal and supplied to the voiceoutput means 112. The number of voice output means 112 corresponds tothe number of other cellular phones and terminal units similarly. Thevoice output means outputs the voice of each terminals.

[0103] Furthermore, the cellular phone 400 is provided with a middleparticipation notice means 114 that is operated when this cellular phoneparticipates in a meeting in the middle, and a middle participationdetection means 113 for detecting a middle participation notice signaltransmitted when the other cellular phone participates in the meeting inthe middle as in the case of the terminal unit in accordance with thefirst embodiment.

[0104] The communication 250 has not only a function to control thecommunication between the cellular phone 400 and a base station but alsoa function to transmit the compressed and coded picture data andcompressed and coded voice data to the network and a function to receivethe compressed and coded picture data and compressed and coded voicedata from the network, namely the two-way function. Furthermore, thecommunication means 250 functions to transmit a middle participationnotice signal to the network and to receive a middle participationnotice signal from the network.

[0105] Because the cellular phone 400 is provided with theabove-mentioned function, it is possible for the cellular phone 400 inaccordance with the present embodiment to participate in a multicastmeeting. The middle participation notice means 114 supplies the middleparticipation information to the communication means 250 through thenetwork when the cellular phone 400 participates in the meeting in themiddle. On the other hand, the middle participation detection means 113receives and detects a middle participation notice signal transmittedfrom the other cellular phone from the network through the communicationmeans 250.

[0106] The notice and detection of middle participation in a multicastmeeting are operated in the same manner as that operated in the firstembodiment. The present invention is applied for potable terminal unitsas the mobile apparatus such as the cellular phone similarly.

[0107] In each embodiment, the in-frame coded “picture” detection unitsare used as the information for detecting middle participation, butotherwise a method in which the rate of the in-frame coded “macro-block”in the picture is detected as the unit to detect middle participationmay be employed. In detail, in the case that the coding format such asMPEG-4 that uses the in-frame coded macro-block is used, not thein-frame coded picture is detected, but the rate of the in-frame codedmacro-block in the picture is detected to detect middle participation.For example, the following detection method is exemplified as a methodfor detecting the in-frame coded macro-block.

[0108] At first, the macro-block coding format in the picture iscounted. Because the coding format information is stored in eachmacro-block, the macro-block coding format can be counted easily byreferring the coding format information. Next, the rate of the in-framecoded macro-block in the picture is counted, and if the rate is equal toa half or more, then it is judged to be the middle participation.

[0109] Furthermore, in each embodiment, the case in which the number ofthe picture decoding means, picture display means, voice decoding means,and voice output means corresponding respectively to the number of otherterminals (hardware or software having such function) are provided isdescribed, but otherwise one hardware or software having such functionperforms these processing by means of time sharing technique in somecases. Therefore, the number of these means is by no means limited.

[0110] Furthermore, in each embodiment, (1) coding method represents thetype of codec (CODEC: COmpression/DECompression) such as H. 261, H 263,or MPEG, (2) coding format represents the difference between thein-frame coding (I-frame) and the inter-frame coding (P-frame), and (3)coding information (coding parameter) represents the picture size, framerate, and bit rate. Furthermore, in (3), the coding information issynonymical for the coding parameter, but in some cases the codinginformation is used to represent the item of attribute and the codingparameter is used to represent the item of attribute value differently(difference between the attribute and attribute value).

[0111] The present invention is described based on the preferredembodiments shown in the drawings, but it will be obvious to thoseskilled in the art that the present invention can be easily modified andchanged in various ways without departing from the spirit and the scopeof the invention. The present invention includes such variousmodifications.

What is claimed is:
 1. A multicast meeting unit comprising: a pictureinput means for receiving a picture stream such as a camera; a picturecoding means for coding the input picture stream to prepare the codedpicture information to be transmitted; a picture transmission means fortransmitting the coded picture information to a network by use of themulticast; a picture receiving means for receiving the pictureinformation transmitted by use of the multicast; a picture decodingmeans for decoding the received data; a picture display means fordisplaying the decoded picture stream; a middle participation noticemeans for notifying the middle participation in a meeting; and a middleparticipation terminal detection means for detecting the terminal thatparticipates in the meeting in the middle, and for supplying theinformation to said picture coding means, wherein said picture codingmeans receives the detection signal from said middle participationterminal detection means, and changes the coding format from thein-frame coding format.
 2. A multicast meeting unit comprising: apicture input means for receiving a picture stream such as a camera; apicture coding means for coding the input picture stream to prepare thecoded picture information to be transmitted; a picture transmissionmeans for transmitting the coded picture information to a network by useof the multicast; a picture receiving means for receiving the pictureinformation transmitted by use of the multicast; a picture decodingmeans for decoding the received data; a picture display means fordisplaying the decoded picture stream; and a participation terminalstoring means for storing the transmitter information on terminals thatare participating in a meeting, wherein said picture receiving means,upon receiving an in-frame coded picture, notifies said picture codingmeans of the reception, and said picture coding means, upon receivingthe notice from said picture receiving means, changes the coding formatto the in-frame coding format.
 3. The multicast meeting unit accordingto claim 2, wherein said picture receiving means, in the case that areceived in-frame coded picture is found to be an in-frame coded picturetransmitted from a terminal other than terminals stored in saidparticipation terminal information storing means by recognizing theterminal with reference to said participation terminal informationstoring means, notifies said picture coding means of the reception. 4.The multicast meeting unit according to claim 2, wherein said picturecoding means, in the case that a notice supplied from said picturereceiving means is found to be an in-frame coded picture received from aterminal other than terminals stored in said participation terminalinformation storing means as the result of reference to saidparticipation terminal information storing means, changes the codingformat.
 5. A multicast meeting unit comprising: a picture input meansfor receiving a picture stream such as a camera; a picture coding meansfor coding the input picture stream to prepare the coded pictureinformation to be transmitted; a picture transmission means fortransmitting the coded picture information to a network by use of themulticast; a picture receiving means for receiving the pictureinformation transmitted by use of the multicast; a picture decodingmeans for decoding the received data; a picture display means fordisplaying the decoded picture stream; and a coding information storingmeans for storing the coding parameter of terminals that areparticipating in a meeting and terminals that participate in the meetingin the middle if a terminal participates in the meeting in the middle,wherein said picture coding means codes the picture data by use of thechanged coding parameter that can be displayed on all the terminals thatare participating in the meeting with reference to said codinginformation storing means.
 6. The multicast meeting unit according toclaim 1, further comprising a priority decision means for deciding andholding the information on the priority of the meeting terminal and forsupplying the information to said picture coding means, wherein saidpicture coding means receives the information from said prioritydecision means and changes the coding format.
 7. The multicast meetingunit according to claim 5, further comprising a significance informationadding means for deciding and holding the information on thesignificance of the information to be transmitted in the meeting and forsupplying the information to said picture coding means, wherein saidpicture coding means receives the information from said significanceinformation adding means and changes the coding parameter.
 8. Themulticast meeting unit according to claim 1, wherein said middleparticipation notice means transmits the middle participationinformation to all the terminals that are participating currently in themeeting by use of the multicast when a terminal participates in themeeting in the middle.
 9. The multicast meeting unit according to claim1, wherein said middle participation notice means transmits the middleparticipation information to all or a part of the terminals that areparticipating currently in the meeting by use of the unicast when aterminal participates in the meeting in the middle.
 10. The multicastmeeting unit according-to claim 1, wherein said middle participationterminal detection means detects an in-frame coded picture transmittedfrom a middle participation terminal.
 11. The multicast meeting unitaccording to claim 1, wherein said middle participation terminaldetection means detects the rate of an in-frame coded macro-blocksupplied from a middle participation terminal.
 12. The multicast meetingunit according to claim 1, further comprising a network error ratemeasurement means for measuring the error rate of the network and forsupplying the information on the error rate of the network to saidpicture coding means, wherein said picture coding means changes thecoding format during the time corresponding to the error rate of thenetwork.
 13. The multicast meeting unit according to claim 2, furthercomprising: a reception notice transmission means for receiving a noticeof the in-frame coded picture reception from said picture receptionmeans and for transmitting a reception notice of the in-frame codedpicture; and a reception notice receiving means for receiving areception notice from said reception notice transmission means and forsupplying the reception notice information to said picture coding means,wherein said picture coding means continues the change of the codingformat until said picture coding means receives said reception noticeinformation.
 14. The multicast meeting unit according to claim 1,wherein said picture coding means changes the changed coding format tothe original coding format after a certain time period elapses.
 15. Themulticast meeting unit according to claim 1, wherein said picture codingmeans codes the picture data by use of coding method corresponding tothe coding method of the received picture.
 16. The multicast meetingunit according to claim 1, wherein said picture coding means codes thepicture data with changing the size to the same size as the size of thereceived picture.
 17. The multicast meeting unit according to claim 1,wherein said picture coding means codes the picture data with changingthe number of frames corresponding to the number of frames of thereceived picture.
 18. The multicast meeting unit according to claim 1,wherein said picture coding means codes the picture data with changingthe data quantity corresponding to the data quantity of the receivedpicture.
 19. The multicast meeting unit according to claim 1, furthercomprising: a voice coding means for coding the voice data and forpreparing the coded voice information to be transmitted; a voicetransmission and receiving means for transmitting and receiving thecoded voice information; a voice decoding means for decoding thereceived voice information; and a voice output means for outputting thedecoded voice data, wherein said voice coding means codes the voice datawith changing the coding method corresponding to the coding method ofthe received voice.
 20. The multicast meeting unit according to claim 1,further comprising: a voice coding means for coding the voice data andfor preparing the coded voice information to be transmitted; a voicetransmission and receiving means for transmitting and receiving thecoded voice information; a voice decoding means for decoding thereceived voice information; and a voice output means for outputting thedecoded voice data, said voice coding means codes the voice data withchanging the coding parameter corresponding to the coding parameter ofthe received voice.
 21. A multicast meeting program for carrying outmulticast meeting by a computer to execute the steps of: inputting apicture stream to a picture input means such as a camera of a multicastmeeting unit; coding the input picture stream by a picture coding meansof the multicast meeting unit to prepare the coded picture informationto be transmitted; transmitting the coded picture information by apicture transmission means to a network by use of the multicast; makinga picture receiving means receive the picture information transmitted byuse of the multicast; decoding the received data by a picture decodingmeans of the multicast meeting unit; displaying the decoded picturestream on a picture display means of the multicast meeting unit;notifying that a terminal participates in a meeting in the middle by amiddle participation notice means, if the terminal participates in themeeting in the middle; and detecting the terminal that participates inthe meeting in the middle by a middle participation terminal detectionmeans of the multicast meeting unit, upon receiving the middleparticipation notice, wherein said picture coding means receives thedetection signal from said middle participation terminal detectionmeans, and changes the coding format from the in-frame coding format.22. A multicast meeting program for carrying out multicast meeting by acomputer to execute the steps of: inputting a picture stream to apicture input means such as a camera of a multicast meeting unit; codingthe input picture stream by a picture coding means of the multicastmeeting unit to prepare the coded picture information to be transmitted;transmitting the coded picture information by a picture transmissionmeans to a network by use of the multicast; making a picture receivingmeans receive the picture information transmitted by use of themulticast; decoding the received data by a picture decoding means of themulticast meeting unit; displaying the decoded picture stream on apicture display means of the multicast meeting unit; and storing thetransmitter information on terminals that are participating in a meetingin a participation terminal storing means, wherein said picturereceiving means, upon receiving an in-frame coded picture, notifies saidpicture coding means of the reception, and said picture coding means,upon receiving the notice from said picture receiving means, changes thecoding format to the in-frame coding format.
 23. A multicast meetingprogram for carrying out multicast meeting by a computer to execute thesteps of: inputting a picture stream to a picture input means such as acamera of a multicast meeting unit; coding the input picture stream by apicture coding means of the multicast meeting unit to prepare the codedpicture information to be transmitted; transmitting the coded pictureinformation by a picture transmission means to a network by use of themulticast; making a picture receiving means receive the pictureinformation transmitted by use of the multicast; decoding the receiveddata by a picture decoding means of the multicast meeting unit;displaying the decoded picture stream on a picture display means of themulticast meeting unit; and storing, in a coding information storingmeans, the coding parameter of terminals that are participating in ameeting and terminals that participate in the meeting in the middle, ifa terminal participates in the meeting in the middle, wherein saidpicture coding means codes the picture data by use of the changed codingparameter that can be displayed on all the terminals that areparticipating in the meeting with reference to said coding informationstoring means.
 24. A cellular phone comprising: a picture input meansfor receiving a picture stream such as a camera; a picture coding meansfor coding the input picture stream to prepare the coded pictureinformation to be transmitted; a picture transmission means fortransmitting the coded picture information to a network by use of themulticast; a picture receiving means for receiving the pictureinformation transmitted by use of the multicast; a picture decodingmeans for decoding the received data; a picture display means fordisplaying the decoded picture stream; a middle participation noticemeans for notifying the middle participation in a meeting; a middleparticipation terminal detection means for detecting the terminal thatparticipates in the meeting in the middle, and for supplying theinformation to said picture coding means; and a communication means forcontrolling the communication between said cellular phone and a basestation, wherein said picture coding means receives the detection signalfrom said middle participation terminal detection means and changes thecoding format from the in-frame coding format, on the other hand saidcommunication means, in addition to communication control betweencellular phone and said base station, transmits the compressed and codedpicture data and the compressed and coded voice data to the network,receives the compressed and coded picture data and the compressed andcoded voice data from the network, furthermore transmits said middleparticipation notice signal to the network, and receives said middleparticipation notice signal from the network.